Final answer:
The expression of male sexually selected traits like ornaments or weapons involves energy and resource costs, which can affect the male's ability to contribute to parental care, as per the handicap principle and good genes hypothesis.
Step-by-step explanation:
The cost relevant to the expression of male sexually selected ornaments or weapons refers to the energy and resources expended in developing and maintaining these secondary sexual characteristics. In species where males have elaborate courtship rituals or colorful plumage, there is a trade-off between attracting mates and providing parental care. For example, the time and energy spent by a peacock on growing a large, vibrant tail may reduce its ability to care for offspring, reflecting a balance between sexual selection and survival. The handicap principle suggests that these costly traits serve as honest indicators of male quality, with healthier or more efficient males being able to afford these ornaments and still survive despite the increased risk of predation.
Contrastingly, if males do not invest significantly in sexual signals, they may have more energy left for other aspects such as parental care. This illustrates the varied evolutionary strategies that different species adopt based on the pressures of sexual selection. The good genes hypothesis explains that females may favor these traits as they indicate genetic superiority, thereby leading to potentially fewer but healthier offspring with increased chances of survival.